Funk Tech Systems (http://www.ozemail.com.au/~budweiser/) can do some great
606 mods based on the Geoff Waterston mods.  They have improved on the
design alot, and added a few extra options not found in the orginal article.
The mods are not just "tweaks" of the original 606 sound, but are fairly
complex redesigns of the architecture.

Here are the details:


Main bass drum has decay, sweep decay, pitch, and sweep amount, with the
sweep being triggered from the High Tom (switchable, so you don't loose the
High Tom sound). Sounds like an 808 bass drum, but with longer decay, and
pitch sweep makes it ideal for drum and bass/jungle loops.

Snare has Noise Filter, Pitch, Decay, and Noise/Pitch Ratio. Sounds can be
either 808 or 909 style snares plus anything in between.

Low tom is switchable to 909 kick drum. Controls include pitch and pitch
sweep.

HiHat / Cymbal bandpass filter control, for weird sounding filter sweeps.

Optional individual outputs for all sounds.

Minimal changes to 606, with only 1 hole needed for cable. (Individual outs
are fitted in the external box).

Original sounds can be recreated.

All pics are on the web site.